A 39-year-old woman was admitted with somnolence, severe hypertension and thrombotic microangiopathy. Both malignant hypertension and thrombotic thrombocytopenic purpura (TTP) were considered. Immediate therapy was instituted to treat both diseases because of severe clinical deterioration. Eventually, TTP was considered less likely due to the presence of grade IV hypertensive retinopathy (papilloedema and soft exudates) and a normal Von Willebrand factor-cleaving protease level. Differentiating TTP from malignant hypertension can be difficult as both diseases have similar clinical, laboratory and radiological features. In both diseases, hypertension, thrombotic microangiopathy and encephalopathy with white-matter lesions in the posterior regions of the brain may be apparent. Funduscopic abnormalities consistent with grade III and IV hypertensive retinopathy are rare in TTP, as are normal levels ofVon Willebrand factor-cleaving protease. Therefore, the diagnosis TTP was considered less likely and plasmapheresis was stopped. Hereafter, the laboratory values pointing towards haemolysis remained normal with adequate blood pressure control supporting the rejection of TTP as the cause of the symptoms.